The use of flexible and articulating gear components such as roller chain, “silent chain” and cog belts within compound gearing systems is well known. One common and well-known application involves connecting two sprocket gears with a roller chain in order to translate force from one sprocket to the other. Roller chain compound gearing efficiently transmits power through the rolling action of the chain rollers during engagement with gear tooth contact, providing frictional advantages over gear tooth-to-gear tooth contact. Roller chain also provides shock resistance accommodation to fluctuating input forces or speeds through expanding and contracting or acting like a spring, thereby providing a means for avoiding responsive damage to the gearing system. Roller chain also provides lubrication system advantages through greater tolerances for accepting a wide variety of lubrications, and will maintain lubrication and run without a case.
Use of a precision roller chain as a ring gear within planetary and epicyclic speed reduction and torque transmission systems has been in use for some time. This application typically requires that the roller chain be fixed to a round or cylindrical solid element in order to align the roller chain into a ring configuration and provide a structural means to receive and transfer forces and speeds. It is common to accomplish this by using a double strand of roller chain, with one of the strands dedicated to form a fixed engagement with a structural element, and the second strand aligned to engage an input or output toothed gearing element, wherein interaction with the gearing element is thereby translated to the structural element. For example, U.S. Pat. No. 3,151,495 to Kurtz and U.S. Pat. No. 3,975,969 to Osborn show various configurations where toothed support members are provided to engage the rollers of a first strand of a twin stranded chain. The first strand is reeved about toothed solid cylindrical elements, the teeth designed to firmly engage the first strand and thereby hold it into a fixed position with respect to the cylindrical element. A second strand engages a second toothed gear or gears, such as a set of planetary sprockets driven by a central sun gear.
One disadvantage with this system is that a single set of planetary sprockets requires a double strand chain ring gear, resulting in space and material inefficiencies. Also, since the support of the roller chain is essentially completely on the rollers of the first strand of the chain, there is a strong propensity of the double chain assembly to cant or tilt when subject to pressure, thus causing the unsupported strand of the chain to be skewed and have less than optimal engagement with the tooth gear member which it is engaging. The greater the pressure on the cantilevered strand, the more detrimental this effect is. Indeed, this is especially detrimental when there is a third strand or chain which engages a third toothed gear.
Another drawback of this configuration is that the first strand rollers engaging the teeth on the support member are not available to mesh with teeth on the second gear, thus requiring a cantilevered structure of at least two strands of chain, one of the strands being engaged on the teeth of the support member, with other, cantilevered strands acting as the meshing device for the tooth gear engagement. Expressed another way, it is not possible to use a single-strand link chain for engaging a single set of planetary sprocket teeth, but rather a chain of at least two strands is required.
It is also known to form a composite internal gear element wherein a single strand of chain is reeved around a disk in a circular arrangement, with the chain link plates supported by the cylindrical outer surface of the disk, while the rollers clear the center or periphery of the disk and are, thus, available for engagement with sprocket teeth on the outside periphery of the roller chain. Huszar (U.S. Pat. No. 3,108,488) teaches a clamp that squeezes the chain and, therefore, chain links against the smooth outer cylindrical surface at the periphery of the disk, with a second or toothed gear engaging the single reeved strand of chain at an external circumference point for gear action, thus permitting external gearing. However, a significant disadvantage of the embodiments taught by Huszar is that they rely solely on friction to hold the chain on a smooth surface to engage the chain with the support member and, under even moderately heavy loads, there tends to be significant slippage, which for many applications is unacceptable. Additionally, this configuration does not allow for internal gearing, such as that provided for by the Osborn '969 and Kurtz devices described above.
Moreover, in this configuration of Huszar, it is extremely difficult to obtain the proper tension on the chain. Too little tension will not result in any significant gripping, and too much will stress the chain beyond its elastic limit, thus causing reduced gripping and out of tolerance parts.
Another patent to Osborn, U.S. Pat. No. 5,456,638, teaches a roller chain reeved about a generally circular disk having a pair of circumferentially-extending spaced link plate receiving grooves. By supporting the roller chain through contact with the chain link plates, a second toothed gear may freely and drivingly engage the chain rollers through engagement at the external circumference of the reeved chain. However, the issue of slippage of the reeved chain with respect to the disk requires additional retaining structures to hold the chain in a fixed position during operation of the device. Embodiments taught include a pin that extends from the exterior of the disk between a pair of rollers to engage the rollers, and a retaining plate device which extends from a flange on the disk between a pair of link plates. And, moreover, if pins are utilized extending between certain of the rollers, the space between the rollers is not available for driving an external connection of a toothed gear and, hence, a double or other multiple-strand chain must be utilized with one strand engaging the disk and the other strand or strands being available to engage a toothed gear.
What is needed is a compound gear that provides the advantages of chain components such as roller chain, “silent chain” and cog belts without the disadvantages of chain cantilevering or skewing responsive to uneven loading across the chain. It is also desired to improve space and material efficiencies by forming a compound chain gear which does not require a first chain strand to engage a support member, thus requiring at least two strands to engage one toothed gear or set of gears. And, lastly, what is needed is an efficient compound roller chain gear wherein each strand of roller chain may be engaged either internally or externally by another gear element.